Revert of Disable Goma for Linux32 (ARM) bots. (patchset #1 id:1 of https://codereview.webrtc.org/2911893002/ )

Reason for revert:
According to crbug.com/726706 this is now fixed so let's give it a try.

Original issue's description:
> Disable Goma for Linux32 (ARM) bots.
>
> This config is having issues to build reliably on Goma.
>
> BUG=chromium:726706
> TBR=mbonadei@webrtc.org
>
> Review-Url: https://codereview.webrtc.org/2911893002 .
> Cr-Commit-Position: refs/heads/master@{#18295}
> Committed: 3a343ad329

TBR=mbonadei@webrtc.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=chromium:726706

Review-Url: https://codereview.webrtc.org/2910963002
Cr-Commit-Position: refs/heads/master@{#18299}

tools_webrtc/mb/mb_config.pyl

@@ -201,9 +201,8 @@
     'gcc_release_bot_x64': [
       'gn', 'gcc', 'release_bot', 'x64'
     ],
-    # TOOD(kjellander): Restore Goma for this when crbug.com/726706 is fixed.
     'debug_bot_arm': [
-      'gn', 'openh264', 'debug', 'arm'
+      'gn', 'openh264_debug_bot', 'arm'
     ],
     'release_bot_arm': [
       'gn', 'openh264_release_bot', 'arm'